In a photolithography step which is one of semiconductor manufacturing steps, a resist is coated in a film shape on a surface of a semiconductor wafer (hereinafter, referred to as a “wafer”) serving as a substrate, and the resultant resist film is exposed in a predetermined pattern and then developed to form a resist pattern.
In the photolithography step, minute unevenness may be present on the surface of the resist pattern developed by a developer, and when an etching processing is performed in the subsequent etching step, the unevenness may adversely affect line width uniformity of the pattern. Therefore, a smoothing processing has been suggested to improve line edge roughness (LER) of the resist pattern or line width roughness (LWR) of the pattern.
The smoothing processing is a processing of exposing the resist pattern to an atmosphere of an organic solvent vapor capable of dissolving the resist so as to swell the surface layer portion of the resist pattern with the solvent vapor. Accordingly, the unevenness of the surface layer portion is dissolved in the organic solvent and smoothed, thereby improving the roughness of the surface of the pattern. Thereafter, a heating processing is performed to remove the organic solvent by evaporation.
Japanese Patent Laid-Open Publication No. 2009-147261 discloses a solvent vapor source that supplies a solvent vapor towards a housing to perform a smoothing processing, the solvent vapor being vaporized by bubbling a liquid solvent stored in a storage tank including a heater with a nitrogen gas (see, e.g., paragraphs 0047 and 0049, and FIG. 8). However, when the solvent vapor in the storage tank is cooled by the nitrogen gas to a temperature lower than that of the liquid solvent, the solvent in the vapor turns back to liquid, which causes variation of the concentration of the solvent vapor supplied to a substrate.